Infernalist Altered Flesh Question

Sup Exiles,

Altered flesh turns 20% cold and 20% lightning dmg and turns it to fire.
It takes 20% pysical as chaos.

Is the math bahind that as simple as saying: I can keep fire res at 75% and the other two on 55% and it would be the same as I would have capped res without the skill?
Furthermore: 20% chaos res on my ring would just balance out the chaos damage I´d recieve?

How do you include the skill in your build?

Greets and (soon) happy holidays!